It is known to store still or video images, for example in image libraries, using representations of objects appearing in images. The representations are used in searching methods to enable images containing objects of interest to be retrieved. The representations may be based on various features of the objects, including colour, texture and shape.
Various methods for representing shapes of objects in images are known. Known methods include chain coding, the quad-tree method and the curvature scale space representation method.
To perform a search in a image searching system, a user inputs a query by presenting the system with a sketch or image of the object sought, or by selecting a view of an object stored on the system. The system then derives or obtains a representation of the query object and compares the query representation with the representations of images stored in the database using an appropriate matching method. The closest matches are displayed on a display unit.
In most cases, an object as it appears in a video image is a projection of a 3-dimensional real object onto a 2-dimensional image plane. The 2-dimensional shape or outline of an object appearing in an image thus depends on factors such as the viewing position, viewing angle and camera and optical system parameters. Objects will therefore have different outlines associated with different views.
A disadvantage of known image database systems is that different views of an object having different outlines are treated as different objects. As a result, for example, if a user inputs a query based on a front view of an object A, and the object A only appears in a video sequence from the rear and side view, no successful matches will result and the object will not be retrieved.